“Honey locusts produce a high quality, durable wood that polishes well, but the tree does not grow in sufficient numbers to support a bulk industry. Its also used for posts and rails since it takes a long time to rot. However, a niche market exists for honey locust furniture. In the past, the hard thorns of the younger trees have been used as nails.

The honey locust is popular with permaculturalists across the globe, for its multiple uses. The legumes make a valuable, high protein cattle fodder, which becomes more readily accessible with the thornless (inermis) variety. The broad shade of the tree canopy is of great value for livestock in hotter climates, such as Australia. It is also claimed to be a nitrogen fixer, by way of rhizobium, which benefits the surrounding soil and plants. The durability and quality of the timber, as well as the ability to produce its own nails, fits the paradigm of self-sustaining agriculture that requires fewer external inputs/resources.

The ability of Gleditsia to fix nitrogen is disputed. Many scientific sources [2][3] [4] clearly state that Gleditsia does not fix nitrogen. Some support this statement with the fact that Gleditsia does not form root nodules with symbiotic bacteria, the assumption being that without nodulation, no N-fixation can occur. In contrast, many popular sources, permaculture publications in particular, claim that Gleditsia does fix nitrogen but by some other mechanism.

There are anatomical, ecological and taxonomic indications[5] to counter the assumption that only nodulating legumes fix nitrogen. Many non-nodulating species are as capable as nodulating species of growing well in nitrogen-limited soils and in some cases grow better. Also their leaf litter and seeds are higher in nitrogen than non-legumes[6] [McKey, 1994; Waterman 1994] and sometimes higher even than nodulating legumes growing on the same site. How this happens is not yet well understood, but current research has recorded by-products of nitrogenase activity in non-nodulating leguminous plants [7] including Gleditsia triacanthos. Also, electron microscopy indicates the presence of clusters around the inner cortex of roots, just outside the xylem, that resemble colonies of rhizobial bacterioids. These may well constitute the evolutionary precursors in legumes for nitrogen fixation through nodulation.”https://en.wikipedia.org/wiki/Honey_locust

Black Locust Trees:
“The wood is extremely hard, resistant to rot and durable, making it prized for furniture, flooring, panelling, fence posts and small watercraft. Wet, newly-cut planks have an offensive odour which disappears with seasoning. As a young man, Abraham Lincoln spent much of his time splitting rails and fence posts from black locust logs. Flavonoids in the heartwood allow the wood to last over 100 years in soil.[7] In the Netherlands and some other parts of Europe, black locust is one of the most rot-resistant local trees, and projects have started to limit the use of tropical wood by promoting this tree and creating plantations. It is one of the heaviest and hardest woods in North America.

Black Locust is highly valued as firewood for wood-burning stoves; it burns slowly, with little visible flame or smoke, and has a higher heat content than any other species that grows widely in the Eastern United States, comparable to the heat content of anthracite.[8] It is most easily ignited by insertion into a hot stove with an established coal bed.[citation needed] For best results it should be seasoned like any other hardwood, however black locust is also popular because of its ability to burn even when wet.[9] In fireplaces it can be less satisfactory because knots and beetle damage make the wood prone to “spitting” coals for distances of up to several feet.[citation needed] If the Black Locust is cut, split, and cured while relatively young (within ten years), thus minimizing beetle damage, “spitting” problems are minimal.

It is also planted for firewood because it grows rapidly, is highly resilient in a variety of soils, and it grows back even faster from its stump after harvest by using the existing root system.[10] (see coppicing)

With fertilizer prices rising, the importance of black locust as a nitrogen-fixing species is also noteworthy. The mass application of fertilizers in agriculture and forestry is increasingly expensive; therefore nitrogen-fixing tree and shrub species are gaining importance in managed forestry.”https://en.wikipedia.org/wiki/Black_locust

“Nitrogen Fixing Trees for Agroforestry

Nitrogen fixation is a pattern of nutrient cycling which has successfully been used in perennial agriculture for millennia. This article focuses on legumes, which are nitrogen fixers of particular importance in agriculture. Specifically, tree legumes (nitrogen fixing trees, hereafter called NFTs) are especially valuable in subtropical and tropical agroforestry. They can be integrated into an agroforestery system to restore nutrient cycling and fertility self-reliance.

On unvegetated sites, “pioneer” plants (plants which grow and thrive in harsh, low-fertility conditions) begin the cycling of nutrients by mining and accumulating available nutrients. As more nutrients enter the biological system and vegetative cover is established, conditions for other non-pioneering species become favorable. Pioneers like nitrogen fixing trees tend to benefit other forms of life by boosting fertility and moderating harsh conditions.

NFTs are often deep rooted, which allows them to gain access to nutrients in subsoil layers. Their constant leaf drop nourishes soil life, which in turn can support more plant life. The extensive root system stabilizes soil, while constantly growing and atrophying, adding organic matter to the soil while creating channels for aeration. There are many species of NFTs that can also provide numerous useful products and functions, including food, wind protection, shade, animal fodder, fuel wood, living fence, and timber, (see chart for specific species yields) in addition to providing nitrogen to the system.”http://www.agroforestry.net/pubs/NFTs.html